Custom Playbook Formation Subs???

It's kind of frustrating to spend so much time making a playbook and can't even use the new (aka returning) formation subs feature.

I know it's not possible in the game, but realistically it should be possible to add right? We can already set our custom playbooks as our default playbooks in the settings, so why can we not add it as our Coach's playbooks in dynasty? All of the formations are already in the game, so I don't see how this was such an oversight.